Thermoplastic ink decorated, polymer coated glass articles

ABSTRACT

A glass article is decorated with a thermoplastic ink which contains no frit. A finely divided heat fusible polymeric coating material is applied to the article over the ink. The article is heated to a temperature at which the particles of coating material fuse to form a smooth continuous film over the ink while the latter is in melted, semi-liquid condition. The melted ink diffuses into (but not through) the polymer film over it, thereby forming a melt-melt bond. The polymeric film imparts a serviceability to the ink which it would not otherwise display.

This application is a continuation of application Ser. No. 573,809,filed May 2, 1975, now abandoned, which in turn was a division ofapplication Ser. No. 440,331, filed Feb. 7, 1974, now U.S. Pat. No.3,937,854, which in turn was a continuation-in-part of application Ser.No. 378,493, filed July 12, 1973, now U.S. Pat. No. 3,937,853.

The invention relates to the decoration of glass articles withthermoplastic inks which ordinarily would not be serviceable for suchuse, and the combining of such inks with a coating by which they aremade serviceable.

In the manufacture of glass articles, it is of course often desirable oressential to apply a decoration to the article. (As used herein, theterm "decoration" is used broadly to mean, without limitation,trademarks, labels, instructions for use, contents, pictures, designs,or other written or printed material. The decoration may be translucent,transparent, or opaque, and may be of one or more colors including blackor white.) Whatever the decoration, it must be serviceable for thenormal use of the article; that is to say, the decoration should notsmear, abrade, rub off, chip, or be removed by whatever type of rinse ordetergent wash the article might be expected to encounter in itsordinary use or in the handling incidental to its manufacture orfilling. Thus, the standard decorating compositions used in labeling popbottles, for example, are formulated to withstand abrasion in fillinglines and in use, and to resist the usual washes and so on.

In order to provide such serviceability or durability, it is the mostcommon practice to decorate glass bottles with a frit-containingcomposition that includes a glassy component which is bonded to theglass surface by firing at high temperature. The fired, enamel-like fritfixes the coloring pigments on the article's surface. Organic inks forglasses are known, which also are united with the glass by firing.

Such compositions or "colors" are most frequently applied by the screendecorating process. For screenability the composition is often made upas a viscous, water-containing slip or, alternatively, as a hot melt orthermoplastic material which is solid at room temperature but becomes ascreenable semiliquid paste when heated to a temperature of about120-200° F. The decorating material, whether water slip or hot melt, isapplied to delineated regions of the glass article by being squeegeedthrough a stencil in the form of a screen of silk or wire which isplaced in registry on the surface of the article. When the screen isseparated from the article, the decorating material remains on thearticle in the delineated area and dries by loss of water (if a slip) orquickly solidifies (if a hot melt). At this stage the decoratingmaterial is very poorly and impermanently adherent to the glass surface,and is a waxy, chalky or powdery layer which is not serviceable. It willsmudge upon contact, and is too easily removable in washing. It becomesdurable and serviceable only if heated so that it fuses and unitesintegrally to the glass.

Thus, in order durably to bond such colors to the glass surface, thescreen decorated article has heretofore had to be subjected to aspecial, high temperature firing step which unites the decoration withthe glass surface. Inorganic frit-containing colors must be fired at atemperature above 800° F., and organic colors at temperatures of350°-500° F. For the inorganic colors this reheating typically requiresa cycle of roughly 45-60 minutes duration. For the organics, the firingcycle is shorter, but in either case there is involved a substantialcapital expenditure (and very substantial space requirements) for theheating equipment and conveyors. Moreover, there is a substantialoperating cost in terms of fuel, article handling and maintenance.However, such firing has been necessary to bond the decoration so as toprovide permanence.

The cost of such decorating materials is relatively high, in large partbecause of the expense of frit or other bonding components and the heattreatment necessary for bonding. This relatively high cost has had theaffect of restricting use of such materials to relatively small surfaceareas or portions of the decorated articles. (Organic colors, which donot require quite such high temperature firing, do not provide theintensity of color or frit bonded colors, and hence are less useful.)Speaking generally, it has not been economically practical to screendecorate a large percent of the decoratable surface area of glasscontainers, at least on the high volume product. For that reason, fritdecorated containers generally do not have large color panels, stripesor designs covering a high percent of their surface area, although froma merchandising standpoint larger color areas would open up newpossibilities for enhancing the appeal and visibility of containers.

This invention is directed to a procedure by which color decoration canbe applied to much larger glass surface areas than would otherwise beeconomically feasible. Much lower cost materials can be used, but theprolonged or high temperature firing cycles that have heretofore beennecessary are avoided. At the same time, the decoration is fullyserviceable, even though it is not united with the glass surface. Thisis achieved with the utilization of colors which are not bonded durablyto the article, and which do not require formulation with the expensivefrit or bonding ingredients that have largely been responsible for therelatively high costs of the decorating colors previously used. Ingeneral, colors can be used which would not, in the absence of anythingmore, adequately resist the abrasion, water or alkali attack to whichthe article is subjected in its ordinary use.

A thermoplastic or hot melt color is used in carrying out the inventionand is applied by the screen decorating technique. It solidifies veryrapidly, almost instantly, on the cooler ware. The color (sometimesreferred to hereinafter as an "ink") is formulated so as to becomesemi-liquid, with a consistency suitable for screening, upon moderateheating. It may be similar to known hot melt colors, except that it canbe and desirably is compounded without the heretofore conventional fritbinding ingredients. Such components are not necessary for bonding and,while they are not harmful, they are not necessary.

Hot melt colors or inks are well known per se and usually include as thevehicle a wax or waxlike material having a melting point between about120° and 200° F. Examples of such waxy vehicle constituents are carnaubawax, paraffin wax, microcrystalline wax, beeswax, palmitic acid, stearicacid, and solid soaps. This is preferably the bulk of the vehicle, e.g.,about 60-85% by weight. The vehicle may also include a binder foradhering the ink to the glass. For example, about 5-25% resin or thelike is useful as a binder and hardener. Ethyl cellulose may also bepresent (e.g., 2-15% of the vehicle) as a viscosity promoter andhardening agent.

The pigment or coloring ingredient incorporated with the vehicle may beparticulate inorganic material, e.g., TiO₂ or Cr₂ O₃, which is insolublein the vehicle, or it may be an organic dye, or a mixture of organic andinorganic colorants. It is desirable to omit any volatiles which wouldhave to be removed for solidification to occur and any solvents whichwould affect the coating resin when the latter is applied. The inkitself does not comprise the invention and its constituents are notcritical. From this disclosure those skilled in the art will readily beable to formulate a variety of suitable thermoplastic inks.

The ink sets up rapidly when applied to the surface of ware which is ata temperature below the screening temperature, for example at ambienttemperature. Second or multiple colors having successively highermelting points can be sequentially overprinted on the first color, inorder to provide a multi-color decoration. None of the layers of ink,however, are permanently boned to the surface of the glass, and theprocess is characterized by the absence of any baking or firingoperation which would unite the decoration to the glass surface as afrit is united. The decoration remains on the glass surface as a waxydeposit, and is easily removable.

A finely divided discrete particle fusible resin is applied over theink. The article is preferably heated for this purpose so that uponcontacting the article, the resin particles will soften or fusesufficiently to become at least partially adherent to it.

The article is then passed through an oven which does not fire or bakethe ink onto it, but which melts both the fusible resin and the ink,causing the resin particles to flow together to form a smooth,continuous film over the ink. At the same time this heating operationcauses some diffusion of the ink into the polymeric film. However, it isimportant that the ink does not migrate entirely through the coatingfilm, to the outside surface. In the final product the ink is protectedby a continuous layer of polymeric coating over it, there being amelt-melt type bond between the solidified resin and ink.

It might be expected that the fusion of a particulate resin over a fluidink would cause undesirable loss of sharpness or blurring of thedecoration. Nonetheless, I have found that this does not occur and ahigh degree of sharpness and distinctness is maintained, and that infact the melted state of the ink during polymer fusion (and optionally,during polymer laydown) facilitates or improves the bond of the polymerto the ink. In this connection, it is advantageous to apply the inkthrough a screen which is 200 mesh or finer (U.S. Standard) screen.Ordinarily, for applying glass frit type decorations, 165 mesh screensare used. This results in a relatively thick lay-down of decoration andthus utilizes a greater amount of material per unit decorated area. Useof screens of smaller mesh sizes has been found feasible in thisinvention, by reason of the omission of particulate frit component. Thisreduces the cost of materials used and also contributes to maintainingsharpness of definition in the product, in that the relatively thinlayer of ink tends to blur less around the edges than a thicker layerwhen the polymer particles impinge on the ink and are fused over it.

The application of polymeric coatings on glass articles, includingcarbonated beverage bottles, is known per se. Such coatings are usefulto protect the glass surface from surface abrasion which otherwise wouldinevitably occur in manufacturing, labeling, filling, packing, and/oruse. The polymeric coating prevents scratching of the underlying glass,which would reduce its strength. The coating also provides a degree ofcushion and thereby softens impact blows which might otherwise causebreakage. Moreover, when applied to a glass container for pressurizedbeverages, the coating resists scattering of glass fragments if thecontainer is broken.

In the past, polymeric coatings have been applied over decorations whichmust first be physically united with the glass and bonded in place. Thatprocedure was recently recommended in Ceramic Industry Magazine,September, 1973, pp. 34-37. In that technique the decoration is notmelted or semi-liquid during fusion of the polymer, and there is nodiffusion of the already hardened decoration into the coating such thata zone or layer of mixed decoration and coating is provided between thedecoration and the coating.

In accordance with this invention, the coating material which is appliedover the ink is a finely divided resin which is fusible at a temperatureat which the ink itself is semi-liquid. By the term "fusible" as usedherein in reference to the coating, is meant that the coating particleswill heat soften so as to flow together or coalesce to form a smooth,continuous film. Preferred for this purpose are the so-called ionomerresins which are ionic copolymers of alpha olefins and alpha,beta-ethylenically unsaturated carboxylic acids, for example of the typedescribed in U.S. Pat. No. 3,264,272. One such ionic copolymer materialwhich is formed from ethylene and methacrylic acid is availablecommercially from DuPont under their trademark "Surlyn", grade AD 5001.This material in particular has been promoted in the market by reason ofits clarity, elasticity and degree of adherence to glass. It begins tofuse (within the above meaning) at about 204° F. It is not a solvent forthe ink, and does not have an adverse chemical affect on the ink. Otherheat-fusible resins which may be used include without limitationpolyethylene, polyvinyl chloride, and ethylene vinyl acetate resins, inpowder form. Such resins may also be prepared as sprayable emulsions,for gun application, with an emulsifier and a vehicle. In this case theresin particles are dispersed in the liquid, but fuse together uponheating, at a temperature at which the ink is semi-liquid. The resin mayalso be prepared as a screenable liquid, for application on a screendecorating machine.

The polymeric coatings can be applied to glass articles by a variety ofcoating techniques. In the coating technique which is presentlypreferred, dry fine particle resin is applied by the electrostatic drypowder spray process. The resin particles are electrostatically chargedoppositely to the glass article (which acts as a ground) and areprojected toward the article by a relatively gentle air current. Theattraction of opposite charges draws the charged particles to thearticle, to which they adhere electrostatically. For this purpose thearticle is desirably heated to about 150°-360° F., which improves theelectrical conductivity of the glass. At such temperatures the adheredresin particles will partially but not thoroughly fuse together. A finalhigher heating is necessary to completely fuse the particles so thatthey coalesce to form a smooth, continuous coating which is adherent tothe glass surface.

Another useful method for applying the polymeric coating to glassarticles is the fluidized bed technique. The resin is maintained as anaereated or fluidized mass while the article, heated to a temperaturesufficient for at least partial fusion of the resin particles, is movedthrough the bed so that it becomes coated, then is removed and heated athigher temperature to coalesce or set the particles and form a smoothcontinuous coating.

Still another type of coating process which can be used is theelectrostatic fluidized bed process. In that process the resin particlesare maintained as a fluidized bed which is electrostatically charged.When the glass article to be coated (which is grounded) is passedthrough the bed of charged particles, the charge tends to adhere theparticles to it. Prior to coating, the glass container is heated forbetter conductivity to a point at which the ink becomes melted, but theheating is not sufficient to effect complete fusion of the resinparticles on the article, and a final heating at higher temperature isused to set the plastic as a continuous smooth coating.

A further description of the invention and its advantages is given inconnection with the accompanying drawings, in which:

FIG. 1 is an axial section of a narrow neck glass bottle decorated andpolymer coated in accordance with the invention, with the relativethicknesses of the ink and the polymer layers greatly exaggerated forpurposes of illustration;

FIG. 2 is an enlarged section showing the zone of interdiffusion of inkand polymer; and

FIG. 3 is a flow diagram illustrating in abbreviated form the steps ofcarrying out a method in accordance with the invention.

The following examples set forth several alternative techniques forcarrying out the invention, but they should not be taken as representingthe only specific processes for doing so.

EXAMPLE I

This example constitutes the presently preferred method of carrying outthe invention for screen decoration of a conventional soda-lime glasspop bottle and then applying a Surlyn coating. The bottles mayoptionally have first been given a standard pyrolytic metal oxide (TiO₂or SnO₂) coating and olefinic lubricity coating, for example asdescribed in U.S. Pat. No. 3,323,889, but this does not affect thedecorating or coating steps.

The decorating color is a non-reactive hot melt or thermoplastic ink. Itcontains a vehicle which is a wax or waxlike material having a meltingpoint of about 120°-200° F., preferably about 165° F. No volatiles(requiring evaporation for the ink to solidify) are present. An organicor inorganic pigment is mixed with the vehicle. No frit is needed andnone is included. The ink would not be serviceable if not protected bythe polymeric overcoat, being deficient in adherence and washresistance. Such inks can be obtained from Drakenfeld Colors, HerculesIncorporated, Washington, Pa., under their designation Hot Organics, andfrom other sources. They are usually supplied in the form of a solidblock which is melted on a heated screen for application, to establish asoft, melted-butterlike consistency for application through the screen.

The decorating color is screened onto the container on a conventionalscreen decorating machine, for example, as manufactured by Carl Strutz &Co., Mars, Pa.; Applied Color Equipment Co., Sapulpa, Okla.; and StarEquipment Co., Washington, Pa. Depending on the particular silkscreening screen printing machine used, the ink may be applied at highrates, e.g., 200 bottles per minute. A further description of hot meltscreen decorating is given in U.S. Pat. No. 2,731,912. A 200 mesh to 300mesh screen is desirable, for minimum ink usage and thickness. Thedecoration may include a label, trademark, printed information, adesign, etc. The squeegeed composition will solidify very rapidly afterwithdrawal of the screen stencil, on a bottle which is essentially atambient temperature, e.g., 72° F. The solidified material is a waxy,somewhat chalky layer which is not united to or bonded on the glass andcan easily be washed or scratched off. Nonetheless, no fusion, bondingor firing step is used; in fact, the ink would not form any better bondwith the glass if it were fired at high temperature. If the inkdecorated but uncoated articles are exposed to a standard simulated linetester (such as the American Glass Research Abuse Line Simulator), theink is so abraded as to be completely unacceptable; similarly, ifexposed to a rinse test to simulate the exposure as given by industrialrinsers (such as the Emhart Rinser), the ink fails. The decoration isnot serviceable unless and until coated.

A number of different colors of ink can be superimposed in quicksuccession on the article to produce intricate multicolor designs ordecorations, using a multiple color decorating machine.

In accordance with the practice of this invention, the resin is applieddirectly over the decoration, without bonding reaction or curing of theink. Preferably, Surlyn resin powder is applied by the electrostatic drypowder spray process. The bottles are carried on a continuous line bychucks which grip them at the finish (i.e., the cap or closure endportion). The bottles are first carried through an oven and preheated toa temperature of about 300°-360° F. (surface temperature as measured byoptical pyrometer). Such heating improves the electrical conductivity ofthe bottles so that they can better act as grounds in the resin coatingstep, which improves the effectiveness of electrostatic coating step.The resin is sprayed by a conventional dry powder spray apparatus, forexample a DeVilbiss Model No. 348, operated at 60 kv DC output. Thesprayed, charged particles adhere to the grounded bottles and partiallyfuse upon contact.

After removal from the spray apparatus, the adherent particulate resinparticles are then set by heating to form a smooth continuous film. Thisis done by passing the bottles through a continuous oven at atemperature of about 390° to 600° F., for a period of 3 minutes to 45seconds. This melts the ink to a semi-liquid state, however the meltedink does not "ball up" or run, but remains in place on the glass as asemi-liquid as the resin particles fuse over it. In the case of Surlyn,the resin also cures or cross-links as it forms the final hardenedcoating. The bottles are air cooled to 250°, then quenched by a waterrinse to about 200° F. (this prevents hazing of the plastic coating).

In the final product, the decorating color is not united to the glass asa frit-containing ink would be. It adheres to the glass like a wax, andis further protected on the glass by the polymeric film over it, whichis bonded to the glass in regions beyond those covered by the decoratingcolor. The polymer coating adds a depth and brilliance to the decorationwhich an uncoated bottle does not display. The coating is much thinnerthan the glass wall, and is suitably about 5 mils thick, but this is notcritical.

If the polymeric coating is carefully removed by stripping or peeling itfrom the bottle, it can be seen that an area of ink remains on thebottle as a thin film, while some of the ink is pulled off with thepolymer. It has diffused into the polymer, not all the way through thelatter, but partially into it. A slanting or wedgelike slice through thefilm makes apparent the interdiffusion of the ink and polymer. This isbelieved to improve the bond of the polymer through the ink. The ink isnot brittle and retains its thermoplastic character, but the coatingprotects it so that the ink is not removed or affected by the ordinaryuse of the bottle.

EXAMPLE II

In this example the polymeric coating is applied to a screen decoratedbottle by the electrostatic fluidized bed process.

The screen decoration is applied as in Example I. After the decoratingstep, the bottles are preheated to about 150°-360° F. (surfacetemperature as measured by optical pyrometer).

The bottles are then carried through an electrostatically chargedfluidized bed of the coating resin particles. The charging apparatus isoperated at 30,000 to 90,000 volts DC. After removal from the bed, theadherent particulate resin particles are then set by heating to form asmooth continuous film. The ink is melted and the adherent particulatematerial is fused over it by passing the bottles through an oven at apeak temperature of 390° F., over a three minute period. The coating iscomplete after cooling.

If the plastic coating is carefully cut and peeled away from the bottle,again it is found that the decorating color is interdiffused with thepolymeric coating. Application of too thick a decoration can causediffusion through the coating, which is often detrimental to appearance.

EXAMPLE III

It should be understood that the invention is not limited to singlecolor decorations. Where two or more colors are to be applied, they areapplied sequentially as hot melts, and set up rapidly. In the subsequentresin fusion step, all of the colors remelt, but they do not mixundesirably or blur during the fusion.

EXAMPLE IV

The coating provides maximum protection for the article if it coverssubstantially the entire surface of the article excepting the finishportion. However, where protection for the article is not a primeconsideration, use of the ink plus coating on even limited areas canprovide a full serviceability of the ink, and a degree of protection forthe glass surface, with minimal cost increase. For example, the coatingmay be applied only to a limited area, so as just to cover thedecoration and a small adjacent glass surface area. For this purpose, itis advantageous to use a polymeric coating composition which itself isscreenable, so that it can be screened on over the coating, preferablyon the same decorating machine as that used to apply the ink. This hasthe advantage of eliminating need for separate coating-applying spray orfluidized bed, or the like. The coating is heated until fused over theink.

While the foregoing examples illustrate various details of embodimentsof the invention in order that others may practice the same, it will beunderstood that the invention is not limited to utilization of thesespecific techniques set forth therein, but may be carried out inaccordance with other techniques within the scope of the followingclaims.

I claim:
 1. A permanently decorated, polymer coated hollow glasscontainer,said container having a surface area thereof with at least onescreen print decoration on it, said decoration being a thermoplastic hotmelt ink which is solid at room temperature and which becomes semiliquidupon heating, a polymer film coating on said container which overliessaid decoration and which covers regions of said container adjacent tothe said surface area on which the decoration is applied, aninterdiffused zone of said decoration and said polymer coating lyingbetween the decoration and the coating, said decoration having anadherence to the glass which is sufficient, in the absence of suchpolymer coating, to permit such coating to be applied over thedecoration without smearing the latter, the adherence of the decorationto the glass being insufficient, in the absence of said polymer coating,to resist removal by such abrasion and alkali attack as is incidental tothe ordinary use of the container, said polymer coating being a smooth,continuous film of a resin which is anchored to and supported by theglass surface regions with which it is in contact, the said decorationbeing meltable at a temperature below that at which the said polymercoating is fusible, the said decoration being melt-on-melt bonded withand diffused into the polymer coating in said interdiffused zone suchthat the decoration would be at least partially removed with the polymercoating if the latter were peeled away from the container, the coatingover the surface area of said container which is covered by saiddecoration being adhered to the glass surface through its bond to thesaid decoration, said decoration being captured by and between the filmcoating and the glass surface.
 2. The container of claim 1 wherein saiddecoration includes a waxy thermoplastic vehicle and a pigment, saiddecoration containing no glass frit ingredient.
 3. The container ofclaim 1 wherein said decoration melts at a temperature between 120° and200° F.
 4. The container of claim 1 wherein said resin is a polymericmaterial which is fusible at a temperature higher than the meltingtemperature of said decoration.
 5. The container of claim 1 wherein saiddecoration is diffused into said film, but not to the outer surfacethereof.
 6. The container of claim 1 wherein said decoration is meltableon said container if said film is stripped away from it.